Control algorithms required in a grid connected photovoltaic generation system may be largely divided into a maximum power point tracking (MPPT) control algorithm, a DC-DC converter input current control algorithm, a phase locked loop (PLL) control algorithm, a DC link voltage control algorithm, an inverter output current control algorithm, an anti-islanding algorithm and an islanding protection algorithm.
Since power of photovoltaic energy is nonlinearly changed depending on amount and temperature of solar radiation, the MPPT control algorithm is a control method of maximizing efficiency by detecting a maximum power point. The DC-DC converter input current control algorithm is performed using input reference current of a DC-DC converter, generated through the MPPT control algorithm. The PLL control algorithm is used to detect phases of a grid connected voltage and to generate output reference current of an inverter. The DC link voltage control algorithm is used to control a DC link current of the inverter to be constant, and generate amplitude of inverter output reference current. The inverter output current control algorithm is performed by generating inverter output reference current according to the phase and amplitude of a DC link voltage generated through the PLL control algorithm and the DC current voltage control algorithm.
Among these control algorithms, the MPPT control algorithm is performed prior to other control algorithms, and therefore requires rapidity and accuracy.